The present invention offers an economical and an environmentally sound method for utilizing chlorosilicon by-products. The chlorosilicon by-products are hydrolyzed to form a particulate silicon containing product and the silicon containing product is added to standard processes for preparing portland cement. The silicon containing product can be used to replace all or a portion of the silicon source typically added to such processes. Use of the silicon containing product in processes for preparing portland cement provides for improved process efficiency.
The preparation of portland cement is well known in the art. Portland cement is a hydraulic cement characterized by the ability to set and harden in water. An essential feature of portland cement is the ability on hydration to form with water relatively insoluble bonded aggregations of considerable strength and dimensional stability. Generally, portland cements are manufactured by processing and proportioning suitable raw materials, burning at suitable temperatures to effect clinker formation, and grinding the resulting hard nodules called clinker to the fineness required for an adequate rate of hardening by reaction with water. Portland cement consists mainly of tricalcium silicate and dicalcium silicate. Primarily, two types of raw materials are required: one rich in calcium, such as limestone, chalk, marl, or oyster or clam shells; the other rich in silicon, such as clay, shale, sand, or quartz.
The present invention is an improved process for preparing portland cement where all or a portion of the silicon supplied to the process by silicon sources such as clay, shale, sand, or quartz is replaced by the silicon containing product resulting from the hydrolysis of chlorosilicon by-products. The use of the silicon containing product resulting from the hydrolysis of chlorosilicon by-products as a silicon source in the process offers advantages over the use of standard silicon sources. First, the friable nature of the silicon containing product provides a material that requires low energy input to mill into an appropriate form for use in the process. Second, the silicon containing product has better reactivity in the cement kiln than standard silicon sources and this translates into reduced fuel consumption due to lower reaction temperatures. Third, when the silicon containing product is formed from organochlorosilicon by-products, the organic component present in the silicon containing product can serve as a fuel source for the process. Fourth, use of the silicon containing product in the process can enhance removal of alkali deposits from the cement kiln preventing detrimental coatings on process equipment and permitting the production of low-alkalinity clinker.
Processes for preparing the silicon containing products useful in the present process are described by Marko, U.S. Pat. No. 4,408,030, issued Oct. 4, 1983, and are incorporated by reference herein.